Core B, Pathology, will provide histologic, immunohistochemical, immunofluorescence, and ultrastructural analyses of animal and human specimens for each project. 1. Morphologic analyses on interaction of neuroblastoma cells and stroma cells in tumor progression, invasion, metastasis, and bone destruction using animal models and human samples (Project 1). 2. Histologic and immunohistochemical analyses of immune-mediated "tumor cell killing" in neuroblastomas by using animal models and human tissues (Project 2). 3. Histologic and immunohistochemical analyses of tumors and normal organs of mice treated with retinoids and modifiers (Project 3). 4. Histologic analyses of neuroblastomas to confirm diagnosis and risk classification, as required by clinical study (Project 4).